On Tue, May 05, 2020 at 10:44:22AM -0700, Nick Desaulniers wrote:
> From: Sedat Dilek <sedat.dilek@xxxxxxxxx>
>
> It turns out that if your config tickles __builtin_constant_p via
> differences in choices to inline or not, this now produces invalid
> assembly:
>
> $ cat foo.c
> long a(long b, long c) {
> asm("orb\t%1, %0" : "+q"(c): "r"(b));
> return c;
> }
> $ gcc foo.c
> foo.c: Assembler messages:
> foo.c:2: Error: `%rax' not allowed with `orb'
>
> The "q" constraint only has meanting on -m32 otherwise is treated as
> "r".
>
> This is easily reproducible via Clang+CONFIG_STAGING=y+CONFIG_VT6656=m,
> or Clang+allyesconfig.
For what it's worth, I don't see this with allyesconfig.
> Keep the masking operation to appease sparse (`make C=1`), add back the
> cast in order to properly select the proper 8b register alias.
>
> [Nick: reworded]
>
> Cc: stable@xxxxxxxxxxxxxxx
The offending commit was added in 5.7-rc1; we shouldn't need to
Cc stable since this should be picked up as an -rc fix.
> Cc: Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx>
> Link: https://github.com/ClangBuiltLinux/linux/issues/961
> Link: https://lore.kernel.org/lkml/20200504193524.GA221287@xxxxxxxxxx/
> Fixes: 1651e700664b4 ("x86: Fix bitops.h warning with a moved cast")
> Reported-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
> Reported-by: kernelci.org bot <bot@xxxxxxxxxxxx>
> Suggested-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>
> Suggested-by: Ilie Halip <ilie.halip@xxxxxxxxx>
Not to split hairs but this is Ilie's diff, he should probably be the
author with Sedat's Reported-by/Tested-by.
https://github.com/ClangBuiltLinux/linux/issues/961#issuecomment-608239458
But eh, it's all a team effort plus that can only happen with Ilie's
explicit consent for a Signed-off-by.
I am currently doing a set of builds with clang-11 with this patch on
top of 5.7-rc4 to make sure that all of the cases I have found work.
Once that is done, I'll comment back with a tag.
> Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
> Signed-off-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> ---
> arch/x86/include/asm/bitops.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
> index b392571c1f1d..139122e5b25b 100644
> --- a/arch/x86/include/asm/bitops.h
> +++ b/arch/x86/include/asm/bitops.h
> @@ -54,7 +54,7 @@ arch_set_bit(long nr, volatile unsigned long *addr)
> if (__builtin_constant_p(nr)) {
> asm volatile(LOCK_PREFIX "orb %1,%0"
> : CONST_MASK_ADDR(nr, addr)
> - : "iq" (CONST_MASK(nr) & 0xff)
> + : "iq" ((u8)(CONST_MASK(nr) & 0xff))
> : "memory");
> } else {
> asm volatile(LOCK_PREFIX __ASM_SIZE(bts) " %1,%0"
> @@ -74,7 +74,7 @@ arch_clear_bit(long nr, volatile unsigned long *addr)
> if (__builtin_constant_p(nr)) {
> asm volatile(LOCK_PREFIX "andb %1,%0"
> : CONST_MASK_ADDR(nr, addr)
> - : "iq" (CONST_MASK(nr) ^ 0xff));
> + : "iq" ((u8)(CONST_MASK(nr) ^ 0xff)));
> } else {
> asm volatile(LOCK_PREFIX __ASM_SIZE(btr) " %1,%0"
> : : RLONG_ADDR(addr), "Ir" (nr) : "memory");
> --
> 2.26.2.526.g744177e7f7-goog
>
Cheers,
Nathan
